Groundwater is often contaminated with gasoline, diesel fuel, and other lighter-than-water compounds or substances, which can form floating layers on the surface of the groundwater if the levels of contamination are high enough. The contamination comes from loss or disposal of wastes or products at or near ground surface, which then leak or leach to the aquifer. The contamination may dissolve into the groundwater as well as float on the surface of the groundwater. Floating contaminants pose a different removal challenge than dissolved contaminants.
Known techniques for removing floating contaminants from the surface of groundwater are less efficient and less successful than would be desirable. Skimmer pumps are commercially available that can be used to remove a floating layer of contaminant. However, available skimmer pumps seem to be less effective when the floating layer is below a minimum thickness. Though some skimmer pumps can remove the floating layer to a thickness of approximately 0.01-inch (sheen), the removal can be slow and require relatively close spacing of wells or the use of trenches dug into the ground to increase the capture efficiency. Trenches are difficult to dig at many sites, where space for such a feature can be lacking. Trenches are also restricted to use at sites with relatively shallow groundwater levels, approximately ten feet or less.
Other substances besides contaminants can also float on the surface of groundwater. For example, a substance intentionally applied to the groundwater for some purpose, such as removing a contaminant by extraction, may form a floating layer on the groundwater. Like contaminants, it can be desirable to remove such substances. However, as with contaminants, such substances can be difficult to effectively and efficiently remove from the surface of the groundwater. The term “floating product” is herein used to describe any such substance, whether contaminant or not, that forms on the surface of the groundwater.